The first imaging study investigating the neuronal processing of odors in humans was published in 1992 and although almost two decades has passed since this seminal study, our knowledge about the central processing of olfactory information remains limited. One factor contributing to this gap in knowledge is the major obstacle of delivering odor stimuli to subjects inside an MRI scanner.
Presenting controlled odorous stimuli to the MRI scanner in a manner suitable for scientific experimentation is difficult due to two overarching factors. First, the environment inside an MRI scanner is hostile to ferrous items, items coated with ferrous material, and any significant amount of metal, ferrous or not. The scanner itself is a powerful magnet (ranging in field strength from 1.5 to 7 Tesla) capable of attracting even minute amounts of ferrous material located within the scanner suite; the force with which these items would be pulled into the scanner bore poses a life-threatening risk for anyone lying inside. Moreover, larger quantities of denser metal in close vicinity to the scanner induce distortions in the acquired images that render them unusable. Therefore, all components placed inside the scanner room must be made entirely out of plastic, wood, and/or limited quantities of aluminum, brass, and/or high-grade stainless steel. Second, stable, controllable airflow and stimulus presentation are required for good measurement. Delivered stimuli preferably display several characteristics, such as a square-shaped form (low, steep rise-time; stable concentration; steep offset), a fast and consistent onset enabling synchronous delivery with other presented stimuli, and a presentation devoid of tactile cues (such as a change in airflow).